Drawing an involute spline 4

[FOSSIE]

Hi, i need a 2D drawing of an involute spline in order for me to be able to cut the internal spline using wire EDM... I understand there is software available that can help with such a task? The spline in question is:

no. of teeth = 18
P.C.D = 1.125"
D.P = 16/32/80
P.A = 30 degrees

I don't have any more data about the spline, but i do have the external spline on a shaft. Is the data i have provided sufficient to draw the spline? and if so can somebody please point me in the direction of the software (or some other way of drawing it....) I think i may need the major/minor diameters also - but i don't have access to very accurate measuring gear, so can i calculate the maj/min dimensions from the PCD/no of teeth?? Ive got vernier callipers - can i just measure the outside diameter of the spline, or is it not that simple? And what about the "tooth thickness"? how can i determine that? (if its needed)

Any advice would be a big help! Somebody must have drawn splines before... If its any use, i have access to AutoCad and Solidworks.

Thanks again
Tom

 

[onestout]

That is just a standard spline. When I draw splines I don't put the involute on because I don't have software to do it and it's not really needed on the drawing anyway, the machine creates the involute when it cuts it. Machineries handbook will have all the info you need on that spline.

Michael

 

[EnglishMuffin]

The sort of spline you are talking about basically has a "half height" gear tooth. There is a bunch of software out there which generates wire EDM gear tooth data. A random search gave me the following (I have no personal experience) :

http://www.edusoft.co.uk/Wire EDM.htm

http://www.hascotech.com/software/dptechnology/esprit-2000/solidwire/solidWire-specifications.htm

http://sofengsvc.com/

Here is a site that goes into some of the problems with wire EDM splines (again, no personal experience) :

http://www.powertransmission.com/gtforums/design/posts/105.html

Also, take a look at thread406-62585 just to see the sort of problems that can arise with wire edm and gear teeth.

 

[diamondjim]

I do have some free autolisp programs that will
allow you to draw the gear in ACAD. You have to
treat the internal spline an the mirror image
of an external gear. Enter the the addendum for
dedendum, the dedendum for the addendum and the
tooth space for the tooth thickness. You will have
to trim the involute at the minor diameter and put
a small fillet in the root at the major diameter.
My e-mail is J.Geisey@juno.com
You will have to look up the major diameter, minor
diameter, and tooth information before you can
draw it. The thread that was mentioned where edm
caused problems was an involute full depth gear.

 

[iaguy]

Back - way before - we had cnc stuff, spline and gear tooling was made by using 3 or 4 arc to approximate the spline. Even in the early 90s I was getting tooling for gears and splines that were created that way.

Finding the radii of the arcs is no hill for a climber.

iaguy

 

[gearguru]

FOSSIE,
you need more data for your spline. Even if it is a standard spline, it can be "side fit" or "OD fit"; then you need to know thetooth thicknesses on both splines, or calculated backlash and known spline tooth thickness. You also should check for clearances between the roots and tips on both splines.

To draw the profile, the following data is needed:
No of teeth
Dia Pitch
Press. angle
circular tooth thickness (at pitch dia)
Major dia
Minor (root) dia

If you give me these data, I can create the *.dxf file for you, you'll be able to open it in any CAD.
I can also create the *.dwg, *.img, *.prt file,if you prefere it. I have my program to do it (not in ACAD, therefore the dxf).
gearguru

gearguru

 

[FOSSIE]

Thanks for all the help guys! I'm new to this game, but learning as we go along. I'll do some homework and find the other parameters you mentioned gearguru.

I'm not sure about the "side fit" or "OD" fit - but the splines engage without needing any force. Instinct tells me its a side fit - since if you examine the used splines, the side "faces" are polished, but the top land is dull (hasnt been touching anything) Am i on the right track here, or have i missed the point of what "side fit" is?

Thanks again, i'll get back to you with the rest of the data as and when i find it.

cheers
Tom

 

[diamondjim]

Most splines are side fit. There is generally
a designation on the drawings to indicate the
type as gear guru suggests as well as the tolerance
range for the circular tooth thickness. Side fit
simply indicates that the clearance is minimal
on the two circular tooth thicknesses and you almost
have a line to line contact but enough to alloy
axial assembly. The nominal circular tooth thickness
would be pi/2 divided by the first number ie by 16.
Class 5 is common standard for side fit. You could
check the male part by using some small pins and take
a measurement over these pins to determine the tooth
thickness of the spline.

 

[FOSSIE]

DIAMONDJIM - can you just go through that trick with the pins in a bit more detail please... I think what your trying to say is place 2 pins against the bottom land of the external spline, and from this i can calculate the major diameter for the internal spline? is that right?

 

[diamondjim]

Fossie,
For someone to cut the spline they needed
to calculate the reading or dimension over
2 pins so they could determine if they were
at the correct tooth thickness.

If you have a gear program that calculates the
dimension over pins, you can keep entering
different tooth thickness starting with the
basic tooth thickness and keep decreasing the
tooth thickness until it agrees with the pin
measurement reading that you have on your part.
I think 7/64 diameter pins would be large enough
to not bottom out in the root.
3mm (.1181)diameter pins might work as well. The pin
size must be large enough to not ride on the tip of the
spline but be making contact on the involute curve.
Your basic tooth thickness would be .09817477.
5 place accuracy should be close enough so use
.09817

 

[gatz]

I'm new to this forum and Monday (8-4-03) I posted a message here.
(It was viewable on this same page and looked ok)
Now, when I look here, it's gone.....what am I doing wrong?

 

[gatz]

Ok, I think I know how to do this posting...

Questions that I have concern involute splines and I've read a few of the pages in the "Gears and Pulley Eng" forum.
I've copied the GEAR.LSP routine by DiamondJim from the 3rd page, but how is this LSP routine started once it's loaded into AuotCad? I get errors on the command line.

Also read about using the formulas that Greg Gill had posted and that confirms what I've been attempting since starting this project to cut the internal spline on wire EDM. I typed up a short BASIC program that solves for the x-y co-ordinates of the involute and outputs as a dxf file, then loaded it into AutoCad; mirrored & rotated the curves so that they coincide with the "circluar space" dimension given in the table on the part print. The problem is; the generated involute curves do not match the sample section of shafting we were given for this job.

We have been trying to assess where the problem lies; whether at our end or the cutomer's.
Any help would be appreciated and I can get the data if someone would like to assist.

 

[diamondjim]

Gatz,
After it is loaded type gear and then
the enter key. All Snaps or Osnaps must be off
as well before typing gear.

 

[gatz]

diamondjim,
here's what I get when loading and attempting to run gear.lsp (btw, I've got acad2000)
.......................................................

Command: Osnap = NONe

Command:
Command:
Command: _appload gear.lsp successfully loaded.


Command: ERROR: extra right paren on input; error: An error has occurred inside
the *error* functionAutoCAD variable setting rejected: "OSMODE" nil

Command:
Command: GEAR
nil

Command:

...........(checking status of OSMODE)

Command: OSMODE

Enter new value for OSMODE <0>: 0

Command: GEAR
nil
.....................................................

gatz

 

[diamondjim]

Gatz,
try this and see if it does the same.
After you type gear, accept all the defaults
the first time and let me know what happens.
Which version of acad are you using?

(defun c:gear ()
(setq numt (getint &quot;Number of Teeth:<24> &quot)
(if (= numt nil)
(setq numt 24))
(setq diap (getreal &quot;Diametral Pitch:<1.00> &quot)
(if (= diap nil)
(setq diap 1.000))
(setq prsa (getreal &quot;Pressure Angle:<20.0> &quot)
(if (= prsa nil)
(setq prsa 20.0))
(setq adum (getreal &quot;Addendum:<1.0000> &quot)
(if (= adum nil)
(setq adum 1.0000))
(setq ddum (getreal &quot;Dedendum:<1.1571> &quot)
(if (= ddum nil)
(setq ddum 1.1571))
(setq tt (getreal &quot;Arc Tooth Thickness :<1.5708> &quot)
(if (= tt nil)
(setq tt 1.5708))
(setq filr (getreal &quot;Fillet Radius:<0.235> &quot)
(if (= filr nil)
(setq filr 0.235))
(setvar &quot;orthomode&quot; 0)
(setvar &quot;coords&quot; 1)
;START CALCULATIONS
;
(setq pnts 19) ;determines involute curve accuracy
(setq prsa (/ (* prsa pi) 180.0)) ;pressure angle to radians
(setq pitr (/ numt (* diap 2.0))) ;calc pitch radius
(setq irad (- pitr ddum)) ;calc inside radius
(setq orad (+ pitr adum)) ;calc outer radius
(setq basr (* pitr (cos prsa))) ;calc base radius of gear
(setq z (- (expt orad 2.0) (expt basr 2.0))) ;three lines of
(setq x (sqrt z)) ;code to make
(setq paodd (atan (/ x basr))) ;an arccosine
(setq incr (/ paodd pnts))
(setq p 0.0)
(setq tt (* diap (/ tt numt)))
(GRAPHSCR)
(setq p2 '(0 0)) ;Center of Gear
(setq x2 (CADR p2))
(setq y2 (CAR p2))
(setq y5 (+ y2 basr))
(setq y6 (+ y2 irad))
(setq p6 (list x2 y6))
(setq p5 (list x2 y5))
(setq pz1 (polar p2 1.95 (* basr 0.9)))
(setq pz2 (polar p2 1.35 (* orad 1.5)))
(COMMAND &quot;CIRCLE&quot; P2 pitr) ;place pitch circle
(COMMAND &quot;CIRCLE&quot; P2 basr) ;place base circle
(COMMAND &quot;CIRCLE&quot; P2 irad) ;place inside circle
(COMMAND &quot;ZOOM&quot; &quot;w&quot; pz1 pz2) ;Window for drawing curve
(setq s (ssadd))
(setq le (entlast))
;
;begin a loop for placement of coordinate pairs
;the command pline will be used to generate a polyline whose
;vertices will be computed by a standard involute curve formula
;
(setq test 0)
(COMMAND &quot;PLINE&quot; p5)
(setq p (+ incr p))
(while (> pnts 0)
(setq e1 (sin p))
(setq e2 (cos p))
(setq e (/ e1 e2))
(setq j (- e p))
(setq x1 (* (/ (sin j) (cos p)) basr))
(setq y1 (* (/ (cos j) (cos p)) basr))
(setq x3 (+ x2 x1))
(setq y3 (+ y2 y1))
(setq p3 (list x3 y3))
(COMMAND p3)
(setq p (+ incr p))
(setq pnts (- pnts 1))
(if (/= test 1)
(PROGN
(setq hyp (sqrt (+ (expt x1 2) (expt y1 2))))
(if (> hyp irad)
(progn
(setq pint p3)
(setq test 1)))))
)
(COMMAND &quot;&quot
(initget &quot;Y y N n&quot
(setq ans Y)
(if (/= ans &quot;N&quot
(PROGN
(setq pz3 (polar p2 (* pi 1.25) (* orad 1.6)))
(setq pz4 (polar p2 (* pi 0.25) (* orad 1.6)))
; (COMMAND &quot;ZOOM&quot; &quot;W&quot; pz3 pz4)
(setq ang13 (/ (sin prsa) (cos prsa)))
(setq ang11 (- ang13 prsa))
(setq x11 (* (sin ang11) pitr))
(setq y11 (* (cos ang11) pitr))
(setq p11 (list x11 y11))
(setq ang (angle p2 p11))
(setq angi (- ang tt))
(setq p12 (polar p2 angi (/ ORAD 0.8)))
(setq beta (angle p2 p3))
(setq ang2 (- (* angi 2.0) beta))
(setq p15 (polar p2 ang2 orad))
(setq adj1 (- ang2 j))
(setq adj2 (+ adj1 (/ (* pi 2.0) numt)))
(setq adj3 (+ adj2 0.3))
(setq p22 (polar p2 adj3 basr))
(setq p17 (polar p2 adj2 irad))
(setq p18 (polar p2 adj2 basr))
(setq angr (* (+ ang11 tt) (/ 180.0 pi)))
(setq p21 (polar p2 ang2 (/ orad 0.8)))
(setq angm (+ angi (/ pi numt)))
(setq p19 (polar p2 angm irad))
(setq p20 (polar p2 angm (+ irad filr)))
(COMMAND &quot;ARC&quot; p15 &quot;c&quot; p2 p3)
; (COMMAND &quot;ARC&quot; p19 &quot;E&quot; P5 &quot;R&quot; filr)
; (COMMAND &quot;ARC&quot; p6 &quot;c&quot; p2 p17)
; (COMMAND &quot;LINE&quot; p2 p12 &quot;&quot
; (COMMAND &quot;LINE&quot; p2 p20 &quot;&quot
(COMMAND &quot;MIRROR&quot; &quot;W&quot; p22 p21 &quot;&quot; p2 p12 &quot;&quot
; (COMMAND &quot;MIRROR&quot; &quot;W&quot; P18 P21 &quot;&quot; P2 P12 &quot;&quot
(COMMAND &quot;ROTATE&quot; &quot;w&quot; pz3 pz4 &quot;&quot; p2 angr)
(while (setq le (entnext le))
(ssadd le s)
)
(COMMAND &quot;ARRAY&quot; s &quot;&quot; &quot;p&quot; p2 numt &quot;&quot; &quot;&quot
) )
(Prompt &quot;\nDone! &quot
(princ)
)

 

[gatz]

diamondjim,

Loaded in your last version and it worked ok, however, the involute lines extend down to the Base Circle and even cross each other. Deleted all but one tooth, then trimmed it to the minor diameter given in the table supplied by customer. Arrayed that as a polyline and looks good.

We've also learned that MasterCam generates these profiles (we weren't sure that involute splines are the same profile as gears). We overlayed MasterCam's profile onto the one your LSP program made and also the one that I had done in BASIC (which generated a dxf). All 3 of these are VERY close...would say within .001/.002 depending on what values are entered for &quot;max actual space width&quot; and OD/ID combinations. (The one yours does and the one that my BASIC program does are within tenths)
We surely appreciate your help in this.
If you'd like, I can send the drawings. They're in ACAD2000 format , but can be saved in earlier versions.

thnx again,

gatz dgatzem@aol.com

 

[leeo]

Hi,
I need to generate a 1 off 2d drawing of an internal involute spline in dxf. format in order to import it to the CAD system Radan.

I was hoping that, if given the details someone would kindly generate this for me and send it in an email, the details of the Involute spline are as follows.

Flat Root Side Fit internal involute spline
number of teeth - 87
module - 2.5400
Pressure angle - 30 deg
base diameter - 191.3743
pitch diameter - 220.980
circular pith - 7.98069
major diameter - 225.9
minor diameter - 218.8

If it is not possible for anyone to generate this for me, then does anyone know a program that is easily accessible to download that i could use.

also I am unsure of the class of the described involute spline and would need to know the importance of it

regards

Lee - lee.oliver@paragon-tools.co.uk

 

[diamondjim]

Lee,
you can use the auto lisp program as
defined earlier by you must reverse the
inputs for the addendum and dedendum
and enter the tooth space instead of the
tooth thickness. Your spline looks like
it has a profile shift. Do you have
the tooth thickness or dimension over
pins?
The program does draw from the base
diameter out to the tip so it would
require alot of trimming but the form
would be accurate. You would also have
to fillet the root as the program
draws a sharp intersection.
This is really a 10 dp system which
is equivalent to 2.54 module.
The program draw either to a 1 dp or
1 module so you would have to divide the
values shown by 2.54 for the program to
work and then scale afterwards by 2.54
to get it to size.
Feel free to call me at 330-678-0226
if you need more information.
An internal gear or spline is simply
a reverse image of an external gear.

 

[gearguru]

leeo,
I can create the file for you - but I need also the tooth thickness (or tooth space) and the diameter where you measure it.
Also please check your calculations - if the circular pitch is measured on the pitch circle, then it should be slightly different (circ. pitch = PI * module)
gearguru

 

[involute]

geez
we cut splines on a wire cut very often and use them as gauges
we do have a gear software and can change pressure angle
and module to suit the data
is easy when you have that
!!!!!!!!!!!!!!!!!!!!